Generally, the present invention is directed to measuring environmental conditions such as pressure, temperature, humidity, velocity, fluid displacements or movement, presence or absence of certain elements in the environment, and the like. Specifically, the presently preferred embodiment of the invention is directed to measuring down hole pressure and temperature of an oil well. It is to be appreciated, however, that the present invention is applicable to a wide spectrum of environmental condition measurement applications both above and below ground. For example, it is believed that the teachings of the present invention are also applicable to anti-pollution measuring applications.
There are a number of down hole pressure and temperature measuring devices known in the art, each having certain advantages and disadvantages. Generally, the prior art devices measure pressure by analog techniques, such as current measurement, and accordingly, the accuracy of the measurement is dependent upon the length of the electrical wire from the measuring device down hole to the remote indicator or recorder which monitors the measurement. This is so, since the length of the wire may vary from well to well due to depth of the hole and the distance of the indicator or recorder from the hole. Also, the resistance of the electrical wire may vary due to temperature variations in the hole. Current leakage may also occur which further degrades the accuracy of the measurement. Another problem is that often times small motors or the like are used with the measuring apparatus which increases the cost as well as the size of the apparatus. Further, calibration accuracy of the known measuring devices is of prime concern due to the above-named variations which have to be compensated for.
According to the present invention, down hole pressure and temperature are concurrently measured utilizing digital techniques in place of analog techniques. Also, radiant energy sources and sensors as well as a relatively small coded wheel are used in place of certain of the analog elements, which is believed to reduce the size of the apparatus while increasing the accuracy of the apparatus. Since the pressure and temperature are concurrently monitored to provide a composite signal indicative of each, the effect of the temperature on the pressure is readily ascertainable. Further, since digital techniques are used rather than analog techniques, the accuracy of the measurement is not effected due to the length of the wire from the hole to the recorder or indicator. The environmental condition measuring apparatus of the present invention is believed to have eliminated or at least substantially reduced the measuring inaccuracies inherent in known devices as set forth above, as well as substantially reducing the size of the apparatus used.